Abstract: The present invention provides a method for efficiently producing a germ-line chimeric animal and a method for conveniently producing a heterozygous animal and a homozygous animal. Specifically, a chimeric animal wherein germ cells are derived from introduced ES cells is produced by injecting embryonic stem cells (ES cells) into an early embryo (blastocyst-stage embryo) incapable of forming germ cells because of a genetic factor. A homozygote is obtained by crossing a female heterozygote with a male heterozygote obtained from the obtained chimeric animals. The thus obtained chimeric animal is extremely useful for conducting gene function analyses and the like.